An Istanbul court on Monday rejected an objection to the jailing of an opposition Republican People's Party (CHP) lawmaker pending an appeal against a 25-year prison sentence for espionage, a judicial source said.

Enis Berberoglu was sentenced to 25 years in jail last Wednesday for allegedly disclosing confidential information involving National Intelligence Organization (MIT) trucks going to Syria in January 2014.

Berberoglu is currently held at Maltepe prison in Istanbul, while he awaits the outcome of his appeal.

The 15th High Criminal Court rejected the objection filed by Berberoglu's lawyer Murat Ergun considering the length of the prison sentence given to the lawmaker, the source said on condition of anonymity due to restrictions over talking to the media.

Berberoglu was convicted of revealing state secrets by passing images to the Cumhuriyet newspaper concerning the search of the MIT trucks which were stopped by local gendarmerie in the southern province of Adana more than three years ago, despite a national security law forbidding such a search.

The Interior Ministry denied at the time that the trucks were carrying arms to groups in northern Syria, saying that in fact they were transporting humanitarian aid to the Turkmen community in the war-torn country.

Berberoglu is the first CHP deputy to be imprisoned in recent years. Around a dozen lawmakers from the Peoples’ Democratic Party (HDP) are currently jailed, mostly awaiting trial over alleged links to the PKK terror group.

In May last year, parliament voted to strip lawmakers facing trial of their parliamentary immunity.